US President Barack Obama directed the EPA to take a tougher line against coal-fred power plants in 2013.

at the Conservative Party’s annual conference that we became necessary to defne a safe level so that fights could recommence. should just accept the climate has been changing for centuries, and any further increases in temperature were And so it is with the two degree dangerous limit – it was only ever intended to allow likely to be quite modest and have a number of benefcial for the continuance of business as usual in the face of the certain knowledge that impacts. industrial activity was driving atmospheric concentrations of greenhouse gases to levels higher than anything in the history of human existence. Two degrees But why now? Why at the very point that the IPCC have The search for energy substitutes was meant to have delivered a solution by now. It removed any doubt about the anthropogenic nature of hasn’t, and time is up; two degrees of warming cannot be avoided under business as climate change would Western decision makers choose usual scenarios. to abandon all pretence that they were ever serious about climate mitigation? The game of charades is now over. It is decision time – capitalism vs observance of the two degree warming limit or, in the very optimistic words of Buckminster Fuller, I would argue it is because the ultimate symbolism of ‘utopia or oblivion’. climate policy now demands a response; the two degree dangerous limit idea. The last month of policy announcements show our political class have made their choice. The promise that climate change won’t become dangerous anytime soon can no longer be deployed to forestall the need for radical action to reduce emissions. Christopher Shaw is an inter-disciplinary researcher at the University of Oxford with That, after all, is what environmental limits are for; not to eight years of experience in research in the area of climate policy, social geography, limit industrial activity, but enable it. public engagement and socio-technical transitions. Follow him @kalahar1

Following Fukushima, safe levels for radiation exposure were increased so that children could go back to schools that, under the previous safety levels, were declared out of bounds.

Aeroplanes were grounded across Europe in 2010 because there was no such thing as a safe level of volcanic ash for planes to fy through. It therefore